a) Field of the Invention
The invention relates to a dual frequency feed assembly and, more particularly, to a dual frequency feed assembly that can simultaneously receive dual frequency signals, or receive and transmit signals at two frequency bands.
b) Description of Related Art
In the past, satellites broadcast signals at Ku-band, which has a low frequency range at about 12 GHz. Due to the increasing need for information, another satellite that broadcasts signals at Ka-band with a higher frequency ranging from 20 GHz to 30 GHz is placed in the same geosynchronous orbit with the Ku-band satellites. Now signals are generally broadcasted at two frequencies, Ka-band and Ku-band, and the reception of these dual frequency signals is still expected to be carried out with just one antenna.
A reflector antenna is often used as a receiving antenna by placing a dual frequency feed assembly at the focus of the reflector antenna to separate the collected signals. Referring to FIG. 1, a feed assembly may include a feedhorn 11 and an orthogonal-mode transducer (OMT) 12. The OMT 12 separates signals in different frequency bands (high and low) and separates signals in different polarizations. The OMT 12 further includes two output/input ports 13, 14, wherein one is high frequency output/input port (Ka-band) and one is low frequency output/input port (Ku-band), and the output/input ports can be further connected to a down converter or act as an input port for a transmitter.
U.S. Pat. No. 5,003,321 discloses a structure having a concentric feed and a plurality of interconnecting waveguides, and the need to simultaneously receive signals in different frequency bands is satisfied thereby. However, the structure of '321 patent is composed of two complex units, which makes mass production difficult. Moreover, it is hard to waterproof the components in the structure, and so signal distortion and attenuation may occur easily.
U.S. Pat. No. 6,714,165 discloses a structure similar to that of '321 patent but with improvement on the division of units, wherein the cutting surface is designed to be in the interconnecting waveguides, and therefore O-ring can be applied for waterproof purpose. However, although the cutting design of '165 patent is more effective in providing water resistance to the structure, the assembly of the structure is still complex in industrial manufacture, and therefore the need and goal for mass production cannot be well met. Furthermore, the two aforementioned conventional technologies only disclose conditions concerning linearly polarized antenna, whereas designs relating to circularly polarized antenna are not mentioned.